The present invention relates to a leader used in automatically developing photographic films and a coupling means for coupling such a leader to films.
When developing films in an automatic film developing machine of the type that utilizes a leader to guide films, films 61 from casing 60 are connected at their leading ends to a leader 62 as shown in FIG. 18. The films 61 are then fed into the machine and are guided by the leader 62.
The leader 62 is a flexible synthetic resin sheet formed with a plurality of equally spaced holes 63 arranged in a feed direction. The holes 63 are adapted to engage a leader feed sprocket provided in the film developing unit.
If a film 61 should separate from the leader 62 and sink into a developing tank filled with developing solution, The film 61 has to be taken out of the tank which interrupts the developing operation. This work is troublesome and time-consuming. Also, there is the possibility that the film might be inadvertently exposed to light while taking it out of the developing tank. In order to prevent such an accident, every film 61 has to be securely connected to a leader 62.
Films 61 are usually connected to the leader 62 by means of splicing tapes 64. But splicing tapes 64 are difficult to handle, firstly because they have to be applied to the films and the leader while placing them on a special workbench to couple them together with high accuracy, and secondly because it is troublesome to detach the tapes from the films and the leader after developing films. The use of such tapes is also disadvantageous from an economical viewpoint because they are not reusable.
U.S. Pat. No. 4110774 discloses a coupling means that requires no splicing tape. Rather, in this arrangement, a film is hooked to a leader as shown in FIGS. 19 and 20. The coupling means shown in these figures includes a tongue 72 defined by two cuts 71 in the rear end of a leader 70 which is formed of a flexible sheet, and an opening 74 formed in the leading end of a film 73. The film is coupled to the leader 70 by inserting the tongue 72 of the leader into the opening 74 of the film so that a neck portion 75 of the tongue engages the side edges of the opening 74.
Since no splicing tape is needed in this arrangement, the film can be coupled to the leader economically. Since the tongue 72 extends rearwardly with respect to the feed direction of the leader 70, it will never get caught or stuck in the film feed path, so that it is possible to feed the leader 70 smoothly through the film feed path. Also, it is possible to couple the film to a desired point on the leader with a high degree of accuracy.
In order to insert the tongue 72 into the opening 74 or to pull it out of the opening 74, the former has to be bent arcuately in the width direction because the width W1 of the tongue 72 is larger than the width W2 of the opening 74.
Such a delicate operation is beyond the capacity of a machine. Thus, in this arrangement, automatic connection and disconnection of the leader and the film are impossible.
While being fed through the film feed path in the automatic film developing machine, the film 73 tends to be subjected to a rather large tensile force at a turning point in the film feed path. Such a tensile force tends to be concentrated on the tongue 72, so that the tongue 72 may be deformed and come out of the opening 74. Thus, this coupling means cannot couple the leader and the film with sufficiently high reliability.
Moreover, since the film 73 is bendable about the neck portion 75 of the tongue 72, it tends to meander and get damaged by being brought into contact with the film feed path.
An object of this invention is to provide a leader and a coupling means for coupling a film to a leader which enable the film to be connected to and disconnected from the leader easily, reliably and, if so desired, automatically.